The aim of the proposed research is to gain a better understanding of the structure and functioning mechanisms of gap junctions and eukaryotic ribosomes. X-ray diffraction studies of two-dimensional crystals of these organelles will be used to confirm structural features determined by electron microscopic methods and relate them to details and events existing in the cell. Low resolution three-dimensional maps from these crystals have already provided some basic information. The protein oligomer in the gap junction membranes - the connexon - appears to be a cylinder of six subunits which are tilted around its axis. Two forms of junction have been found. Differences between them in terms of the configuration of the connexon subunits suggest a mechanism by which the junction might function in vivo. We propose now to confirm these findings and to obtain a more precise description of the mechanism by X-ray diffraction of oriented pellets. In addition we shall use X-rays to relate the two forms to details present in functioning tissues. The map obtained from the crystalline ribosomes shows how they are oriented on, and attached to, endoplasmic reticulum membranes. A new two-dimensional ribosome crystal, space group P4212, has been grown in vitro which will enable analyses to be conducted at higher resolution. We shall now investigate the overall shape of the ribosome and the distribution of RNA and protein. X-ray diffraction measurements will be used to supplement data collected by electron microscopy and provide a direct correlation of features determined in an artificial environment with features present in solution.